A Model of the Oxidation of Polycyclic Aromatic Compounds in Cloud and Fog Droplets

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the atmosphere. PAHs are oxidized in the atmosphere to produce (among other species) oxy-PAHs or PAHs with one or more oxygen atoms. The role of clouds and fogs and their influence on the abundance of oxy-PAHs in the atmosphere have been previously studied. This work presents a computer model that predicts PAH reaction and oxy-PAH / PAH partitioning in the suspended droplet phase in the atmosphere. A FORTRAN model that had previously been used for modeling non-aromatic species was adapted to PAH and oxy-PAH. Concentrations of PAH and oxy-PAH comparable to those reported in fogs and clouds were used. Partitioning between the droplet and gas phases was investigated with calculated Henry's law constants, octanol-air partition coefficients, and octanol-water partition coefficients. Literature photooxidation rates were incorporated for PAH loss. The production of oxy-PAH was modeled using experimentally determined rates in simulated solar irradiation. This work builds upon prior research by calculating the loss of PAH species and gain of oxy-PAH in a representative cloud and fog droplet.